1. Field of the Invention
The present invention relates to a cylindrically shaped fiber holder that holds a fiber along its primary axis. The holder and associated rotation system allow a conventional motor to precisely rotate a fiber, e.g., an optical fiber, about its longitudinal axis.
2. Discussion of Related Art
Optical fibers are the basis of fiber optical communication systems. While their use is already ubiquitous, it is expected to increase in the future. In order to optimize the use of optical fibers, a number of different type of optical fibers have been developed. One class of optical fibers, referred to as polarization maintaining (PM) optical fibers, is made up of optical fibers that are not rotationally symmetric. PM optical fibers are useful in many applications, such as optical systems, fiber sensors, and coherent optical devices. The cross section of type of PM optical fiber is shown in FIG. 1(A).
The optical fiber 101A shown in FIG. 1(A) is commonly referred to as a xe2x80x9cpandaxe2x80x9d fiber. It has a core 103A, and two oppositely positioned, cylindrically shaped regions of highly doped glass 105A. These regions 105A apply stress on the core 103A. Because of this stress, the fiber 101A achieves two orthogonal principal axes with different refractive indexes, causing different light velocities. Linearly polarized light that is injected into the fiber with its polarization direction parallel to one of the different axes of the fiber will remain parallel to the axis along the length of the fiber. Thus, before two polarization maintaining fibers can be spliced together, the polarization axes of the fibers must be aligned to prevent signal loss across the resulting splice. Accordingly, at least one of the fibers must be rotated about its longitudinal axis to match the alignment of the other fiber.
Other types of polarization maintaining fibers are shown in FIGS. 1(B)-1(D). The PM fiber 101B illustrated in FIG. 1(B), referred to as a xe2x80x9cbowtiexe2x80x9d fiber, also has a core 103B and two oppositely positioned stress-applying portions 105B. The PM fiber 101C shown in FIG. 1(C) has a core 103C surrounded by an elliptical cladding 105C, while the PM fiber 101D shown in FIG. 1(D) simply has an elliptically shaped core 103D.
In order to splice a polarization maintaining optical fiber 101 to another with the conventional method, the fiber 101 is first positioned in a fiber holder, such as the fiber holder 201 shown in FIGS. 2(A) and 2(B). The fiber holder 201 has a body 203, which defines a recess 205 for holding the fiber 101. It also has a hinged cover 207 for securing the fiber 101 in the recess 205. As seen in FIG. 2(B), the cover 207 has a number of pads 209 for holding the fiber 101 in place within the recess 205.
Turning now to FIG. 3, when the fiber 101 is to be spliced to another fiber, the holder 201 is mounted on a holder mount 301. The holder mount 301 is connected to a rotation shaft 303, which in turn is connected to a gear 305 with teeth 307. The teeth 307 of gear 305 engage the teeth of another gear 311. Gear 311 is connected by a drive shaft 313 to a motor 315. Thus, when the motor 315 turns the gear 311 through the drive shaft 313, the gear 305 rotates the fiber holder 201 on the fiber mount 301 through the drive shaft 303. In this manner, the motor 315 rotates the fiber 101 about its longitudinal axis to align it for splicing.
One problem with this prior art arrangement is the precision of the rotation. Even very short operations of the motor 315 can over-rotate the fiber 101, preventing its proper alignment.
To address this problem, the prior art has employed precision-operated motors, such as stepper motors, to control the rotation of the holder mount 301. While these precision motors offer some improvement over conventional electrical motors, they still do not provide sufficient precision to accurately rotate the fiber 101 for alignment. Moreover, precision motors can be prohibitively expensive for some applications. Accordingly, there is a need for a relatively inexpensive structure that allows an optical fiber 101 to be precisely rotated about its longitudinal axis for alignment with another fiber.
The invention provides a rotator and associated system that can precisely rotate a fiber about its longitudinal axis for alignment with another fiber. Moreover, the invention allows the fiber to be precisely rotated with a relatively imprecise, conventional electric motor.
According to one aspect of the invention, a cylindrically shaped rotator is provided that can hold either a fiber or a fiber holder along its central axis. The rotator is driven by a drive roller running parallel to the central axis of the rotator. The diameter of the portion of the drive roller that operates on the rotator is much smaller than the diameter of the rotator, so that even large rotational movement of the drive roller produces only small rotational movement of the rotator. Preferably, the diameter of the rotator is 2 to 6 times larger than the effective diameter of the drive roller.
With one aspect of the invention, the rotator has a friction band wrapped about its circumference. The drive roller then contacts the friction band directly to rotate the rotator. With another aspect of the invention, the drive roller is connected to the rotator by a belt, chain, gear or the like.
According to yet another aspect of the invention, the rotator has markings on its surface, so that the rotational orientation of the rotator and rotational movement of the rotator can be identified. With some embodiments of the invention, the markings are binary markings that can be automatically recognized by, for example, a conventional bar code reader.